Hypodermic cannulas are manufactured by the millions for the many medical uses including blood and solution administration and collection, blood sample taking, and fistula needles for taking and returning blood for processing in a hemodialyzer or the like.
It is known that the best needles from the viewpoint of patient acceptance are the sharpest needles. However, the manufactureability of the needle is also an important factor since commercially successful needles will be manufactured by the millions. Also, such needles must be manufactured with great uniformity from unit to unit, and desirably are highly inexpensive in their manufacturing process.
The expired Deluca U.S. Pat. No. 3,308,822 shows a hypodermic needle having a sharp tip which is formed by five separate cuts of a shaping tool. Such a needle may exhibit certain desirable characteristics of sharpness, but the five separate cuts represent an undue level of complexity in the manufacturing process. Also, the cutting edge extending from the point extends to the outer wall of the cannula.
However, in needles providing vascular access, sharpness can be a problem. In this situation the point of the cannula must rest within the walls of a vessel, but the angle of the point is downward as the needle has been inserted through the skin at an angle. If the cannula is pushed downward, the sharpened point may touch the inside lumen of the vessel. If it pierces the lumen of the vessel a haematoma will result.
Tersteegen et al U.S. Pat. No. 4,368,738 teaches a bent point cannula to try to avoid this problem. A well-known three bevel sharpened cannula is formed, and then the tip of the cannula is bent upwards much like a ski tip. If the cannula is pushed downward, it is likely that only the underside of the bent-portion will touch the lumen but not damage it.
There are many other problems with this approach. Not only is it very costly to bend a point, but the point can be easily damaged if this operation isn't performed precisely. Also, the bent point requires the cannula be inserted through the skin with the bevel in an abnormal "upside-down" position. Only after the point and bevel is completely within the vessel is the bevel turned "right-side up". In clinical practice, this has shown to be more dangerous than the problem it sought to avoid.
Zimmerman U.S. Pat. No. 5,290,267 and Hickey U.S. Pat. No. 2,697,438 also show similar bent points.
By this invention, a cannula or needle is provided having a simplified manufacturing process, which exhibits extreme incision sharpness for maximized patient comfort, but also protection from haematomas, by means of the point and all forward cutting edges are spaced inwardly from the cannula outer wall.